Duncan Chard/Bloomberg via Getty Images(TOKYO) -- Boeing's grounded fleet of 787 Dreamliners will resume flying within weeks, company executives said on Friday, after Boeing engineers developed layers of additional safety measures to eliminate the risk of fire from a faulty lithium-ion battery system.

Speaking to reporters in Tokyo, Chief Engineer Michael Sinnett fiercely defended the Dreamliner, calling it "among the safest airplanes" in Boeing's history. He said engineers had spent 200,000 hours analyzing what caused batteries on two of its flights to overheat in January.

In one incident, a lithium ion battery caught fire on a Japan Airlines flight parked at Boston's Logan Airport. Smoke from a battery system on an All Nippon Airways flight in Japan forced an emergency landing and prompted U.S. and Japanese regulators to ground all 50 Dreamliners indefinitely.

"We may never get to the single root cause [of the problems]," Sinnett said. "But the process we've applied to understand what improvements can be made is the most robust process we've ever followed in improving a part in history."

In Boeing's first detailed explanation of the proposed changes to the battery system, Sinnett said engineers had identified 80 potential problems that could lead to a battery fire and redesigned the system to eliminate any fire risk.

Boeing plans to add a battery enclosure made of stainless steel, preventing any gas released from the batteries from spreading to the rest of the plane. Engineers also plan to add heat-resistant sleeving, and extra insulation spacers.

Sinnett said he was "confident" a fire would not occur, but that he could not rule out battery failures in the future.

"Parts fail. We know that some day a battery may fail," he said. "We need to make sure that there is no significant impact at the airplane level when it does."

The new system has already gone through a third of the tests required for the certification process, and will likely be completed "within weeks," according to Boeing Executive Vice President Ray Conner, who also spoke in Tokyo.

But Japanese Transport Minister Akihiro Ota failed to provide a timeline of the Dreamliner's return, saying the Transport Ministry still had to conduct tests and analyses with the Federal Aviation Administration to confirm the safety of the aircraft.